1. Technical Field of the Invention
The present invention relates to the general field semiconductor devices and, more particularly, to integrated-circuit chips equipped with projecting external electrical contact pads.
In one application, such chips are intended to be mounted on boards so that their external contact pads establish electrical connections on these boards. To this end, during assembly, the chips are pressed in the direction of boards provided with a dielectric layer having particles of an electrically conductive material in suspension, so that the particles lying between the boards and the end or front faces of the external contact pads establish the electrical connections.
In another application, such external contact pads are intended to be soldered to the end of overhanging electrical connection tracks carried by flexible strips. In order to carry out such assembly, the electrical connection track ends are pressed onto the upper face of the contact pads of the chips, at a relatively high temperature.
2. Description of Related Art
Currently, based on a chip comprising a lower layer on which internal pads are formed and a superficial layer which covers the latter and which has surface bumps in the zones of these internal pads, openings are produced in the superficial layer above the internal pads, and the external and projecting contact pads are produced by growth deposition of an electrically conductive material in the openings of the superficial layer and the openings of a temporary mask, which are larger than the openings of the superficial layer. The result is that the end faces of the external contact pads which are obtained have a hollowed central part and a peripheral rim corresponding to the rim of the superficial layer enclosing the corresponding opening made in this layer.
Such an arrangement causes weakening of the superficial layer around the external contact pads and a risk of cracks appearing during the aforementioned assembly operations, which need to be carried out at a relatively high pressure particularly because of the existence of the hollowed parts, these cracks being conducive to the appearance of internal corrosion of the chip. Furthermore, since the internal pads are generally made of aluminum and the external contact pads are generally made of gold, there is a risk of electrochemical reactions which, by expanding the material, are liable to damage the electrical connections and further increase the risk of cracks appearing.
There is a need in the art to improve the mechanical strength of integrated-circuit chips with projecting external contact pads, in respect of both pressure and temperature, particularly during the operations of connecting the pads to other connection means.